Composition from reacting vinylidene terminated polybutadiene/acrylonitrile and bisimide

ABSTRACT

A novel method for preparing a thermosetting imide resin composition which consists of chemically reacting a liquid mixture of a carboxy-(CTBN) or vinylidene-(VTBN) polybutadiene/acrylonitrile and a co-reactant comprising 
     a. at least one N,N&#39;-bisimide of an unsaturated carboxylic acid of general formula I ##STR1##  wherein B represents a divalent radical containing a carbon-carbon double bond and A represents a divalent radical having at least two carbon atoms, or 
     b. the imide resin reaction product of an least one N,N&#39;-bisimide of general formula I and at least one primary organic diamine or organic hydrazide, or 
     c. the imide resin reaction product of at least one N,N&#39;-bisimide of general formula I, at least one monoimide, and at least one organic hydrazide, 
     to yield a thermosetting imide resin composition containing copolymerized CTBN or VTBN and co-reactant. A resin composition prepared by this method may be cured at a temperature between 100° C. and 350° C. to yield a full cross-linked polyimide matrix containing a dispersion of phase-separated solid particles of copolymerized CTBN or VTBN and co-reactant.

This is a continuation of application Ser. No. 113,322 filed Oct. 28,1987, now abandoned, which is a continuation of Ser. No. 747,460 filedJune 21, 1985, now abandoned, which is a continuation-in-part of Ser.No. 645,311 filed Aug. 21, 1984, as the U.S. national stage ofInternational Application No. PCT/GB83/00350, filed Dec. 23, 1983, nowabandoned.

This invention relates to thermosetting imide resin compositionscontaining elastomers, to methods of preparing these compositions, andto elastomer-toughened polyimides cured from these composition. Inparticular but not exclusively, this invention is concerned with theelastomer-toughening of addition-type polyimides which are produced fromthe polymerisation and crosslinking of bismaleimide prepolymers.

Thermoset polyimides are organic polymers which in general have veryhigh thermal and oxidative stabilities. They are used in a number ofindustrial applications, especially as adhesives and structuralcomposites. Most polyimides fall within the category of addition-type orcondensation-type polyimides according to the type of polymerizationreaction which produces them from their prepolymer constituent orconstituents. Condensation-type polyimides are generally produced fromdianhydrides and diamines via the formation of a soluble polyamic acidprecursor. The formation of the polyimide from the polyamic acid isknown as cyclodehydration and entails the liberation of water which,under the reaction conditions, is liberated as a vapour which can createvoids in the polymer. Addition-type polyimide prepolymers are cured byan addition reaction which overcomes the problem caused by volatileevolution of water, and thus addition-type polyimides possess asignificant advantages over condensation type polyimides.

One disadvantage of addition-type polyimides however is that they dependto a large degree on a highly crosslinked structure for high temperaturecapabilities, which structure can result in brittle behaviour. Some ofthe more brittle addition-type polyimides have been toughened by thechain extension of the imide prepolymer molecules, which has resulted inthe polyimides cured therefrom having more open flexible molecularstructures than their unmodified, brittle counterparts. However, thisincrease in toughness has usually been found to be offset by a majorreduction in other desirable properties of the polyimides, such as glasstransition temperature, thermal stability and mechanical strength,because chain extension of the prepolymer reduces the density ofinter-molecular cross-links in the polyimide structure.

Attempts have been made to improve the toughness of addition-typepolyimides by the addition of elastomers. St Clair et al (Int JAdhesion, July 1981 page 249) reported an up to 5 fold increase in thetoughness (in terms of increased fracture energy) of an addition-typepolyimide prepared from a bisimide prepolymer having nadic end groups,by the addition of either aromatic amine-terminatedbutadiene/acrylonitrile (AATBN) or aromatic amine-terminated silicone(AATS) to the prepolymer. However, one disadvantage of using either ofthese two elastomers in that they do not appear suitable for tougheningsome other types of addition-type polyimides. Gollob et al(Massachusetts Institute of Technology School of Engineering ResearchReport R79-1, August 1979) reported that the toughness of abismaleimide-type polyimide was little changed by the addition of eitherof these two elastomers to the bismaleimide prepolymer prior to curing.

It is one object of the present invention to provide a novel method forpreparing an elastomer-toughened polyimide whereby the abovedisadvantage is overcome or at least mitigated in part. Other objectsand advantages of the present invention will be evident from thefollowing detailed description thereof.

According to a first aspect of the present invention there is provided amethod for preparing a thermosetting imide resin composition whichcomprises chemically reacting a liquid mixture of afunctionally-terminated polybutadiene/acrylonitrile (--TBN) polymercomprising either a carboxy-terminated polybutadiene/acrylonitrile(CTBN) or a vinylidene-terminated polybutadiene/acrylonitrile (VTBN),and of a co-reactant comprising

(a) at least one N,N'-bisimide of an unsaturated carboxylic acid ofgenerally formula I ##STR2## wherein B represents a divalent radicalcontaining a carbon-carbon double bond and A represents a divalentradical having at least two carbon atoms, or

(b) the imide resin reaction product of at least one N,N'-bisimide ofgeneral formula I and at least one primary organic diamine or organichydrazide, or

(c) the imide resin reaction product of at least one N,N' bisimide ofgeneral formula I, at least one monoimide, and at least one organichydrazide,

to yield a thermosetting imide resin composition containingcopolymerised TBN polymer and co-reactant, said composition beingcurable at a temperature between 100° C. and 350° C. to a fullycrosslinked polyimide matrix containing a dispersion of phase-separatedsolid particles of copolymerized TBN polymer and co-reactant. The matrixpreferably has a lap shear strength at 20° C. at least 50% greater thanthat of a fully crosslinked polyimide cured from the co-reactant alone.

Since the rate of homopolymerisation of the co-reactant is temperaturedependent, it is important that the temperature selected for the TBNpolymer/co-reactant copolymerisation reaction is low enough for theco-reactant to remain in a ungelled state for a sufficient length oftime to allow the TBN polymer to copolymerise with he co-reactant andform into phase-separated particles in the reaction mixture within thattime. For this reason, the copolymerisation reaction is convenientlycarried out at a temperature in the range of 100°-200° C. (provided ofcourse that both the co-reactant and the TBN polymer are in a liquidstate at the temperature selected), preferably below 150° C.

In the at least one bisimide of general formula I, the group B ispreferably selected from ##STR3## and more preferably the at least onebisimide comprises at least one of the following bisimides:

1,2-bismaleimido ethane,

1,4-bismaleimido butane,

1,6-bismaleimido hexane,

1,12-bismaleimido dodecane,

1,6-bismaleimido-(2,2,4-trimethyl)hexane,

1,3-bismaleimido benzene,

1,4-bismaleimido benzene,

4,4'-bismaleimido diphenyl methane,

4,4'-bismaleimido diphenyl ether,

4,4'-bismaleimido diphenyl sulfide,

4,4'-bismaleimido diphenyl sulfone,

4,4'-bismaleimido dicyclohexyl methane,

2,4- bismaleimido toluene,

2,6-bismaleimido toluene,

N,N'-m-xylylene bismaleimide,

N,N'-p-xylylene bismaleimide,

N,N'-m-phenylene biscitraconic acid imide,

N,N'-4,4'-diphenylmethane citraconimide, and

N,N'-4,4'-diphenylmethane bisitaconimide.

The co-reactant may comprise the reaction product of the at least onebisimide of general formula I and at least one primary organic diamineof general formula II

    H.sub.2 N--D--NH.sub.3                                     II

wherein D represents a divalent radical having not more than 3 carbonatoms, provided that the ratio of the total number of moles of bisimideof general formula I to the total number of moles of diamine of generalformula II in the reaction mixture lies in the range 1.2:1 to 50:1. Suchreaction products and methods of preparation thereof are disclosed inU.S. Pat. No. 3,562,223. Examples of diamines of general formula IIwhich may be employed, are 4,4'-diaminodicyclohexylmethane,1,4-diaminocyclohexane, 2,6-diaminopyridine, metaphenylene-diamine,paraphenylenediamine, 4,4'-diaminodiphenylmethane,2,2-bis(4-aminophenyl)propane, benzidine, 4,4'-diaminophenyl oxide,4,4'-diaminodiphenyl-sulphide, 4,4'-diaminodiphenylsulphone,bis-(4-aminophenyl)di-phenylsilane, bis-(4-aminophenyl)methylphosphineoxide, bis-(3-aminophenyl)methylphosphine oxide,bis-(4-aminophenyl)phenylphosphine oxide,bis-(4-aminophenyl)phenylamine, 1,5-diaminonaphthalene,metaxylylene-diamine, paraxylylene diamine,1,1-bis(paraaminophenyl)phthalene, and hexamethylenediamine.

Alternatively, the co-reactant may comprise the reaction product of theat least one bisimide of general formula I and at least one organichydrazide of general formula III ##STR4## wherein E represents adivalent organic group, provided that the ratio of the total number ofmoles of bisimide of general formula I to the total number of moles ofhydrazide of general formula III in the reaction mixture lies in therange of 1.1:1 to 1:1. Such reaction products and methods of preparationthereof are disclosed in U.S. Pat. No. 4,211,860. Examples of hydrazidesof general formula III which may be employed include

Oxalic acid dihydrazide,

malonic acid dihydrazide,

succinic acid dihydrazide,

glutaric acid dihydrazide,

adipic acid dihydrazide,

pimelic acid dihydrazide,

suberic acid dihydrazide,

sebacic acid dihydrazide,

cyclohexane dicarboxylic acid dihydrazide,

terephthalic acid dihydrazide,

isophthalic acid dihydrazide,

2,6-naphthalene dicarboxylic acid dihydrazide, and

2,7-naphthalene dicarboxylic acid dihydrazide.

The co-reactant may also comprise the reaction product of the at leastone bisimide of general formula I and at least one organic hydrazide ofgeneral formula IV ##STR5## wherein G represents a divalent organicgroup, provided that the total number of moles of bisimide of generalformula I to the total number of moles of hydrazide of general formulaIV lies in the range 1.1:1 to 10:1. Such reaction products and methodsof preparation thereof are disclosed in U.S. Pat. No. 4,211,861.Examples of hydrazides of general formula IV which may be employedinclude

Amino acetic acid hydrazide,

alanine hydrazide,

leucine hydrazide,

isoleucine hydrazide,

phenyl alanine hydrazide,

valine hydrazide,

β-alanine hydrazide,

γ-amino butyric acid hydrazide,

α-amino butyric acid hydrazide,

ε-amino-caproic acid hydrazide,

amino valeric acid hydrazide,

and other aliphatic amino acid hydrazides.

Aromatic amino acid hydrazides such as

p-amino benzoic acid hydrazide,

p-amino benzoic acid hydrazide,

m-amino benzoic acid hydrazide,

anthranilic acid hydrazide, may also be used.

As a yet further alternative, the co-reactant may comprise the reactionproduct of the at least one bisimide of general formula I, at least onemonoimide of general formula V ##STR6## wherein B represents a divalentradical containing a carbon-carbon double bond and J represents analkyl, cycloalkyl, or aryl group, and at least one organic hydrazide ofgeneral formula III ##STR7## wherein E represents a divalent organicgroup. Such reaction products and methods of preparation thereof aredisclosed in U.S. Pat. No. 4,303,779.

Examples of hydrazides of general formula III which may be employedinclude

Oxalic acid dihydrazide,

malonic acid dihydrazide,

succinic acid dihydrazide,

glutaric acid dihydrazide,

adipic acid dihydrazide,

pimelic acid dihydrazide,

suberic acid dihydrazide,

sebacic acid dihydrazide,

cyclohexane dicarboxylic acid dihydrazide,

terephathalic acid dihydrazide,

isophthalic acid dihydrazide,

2,6-naphthalene dicarboxylic acid dihydrazide, and

2,7-naphthalene dicarboxylic acid dihydrazide.

Examples of monoimides of general formula V which may be employedinclude

N-methylmaleimide,

N-ethylmaleimide,

N-propylmaleimide,

N-dodecylmaleimide,

N-isobutylmaleimide,

N-isopropylmaleimide,

N-phenylmaleimide,

N-phenylcitroconimide,

N-phenylitaconimide,

N-toluylmaleimide,

N-mono-chlorophenylmaleimide,

N-biphenylmaleimide,

N-naphthlymaleimide,

N-vinylmaleimide,

N-allylmaleimide, and

N-cyclohexylmaleimide.

Where the co-reactant comprises the imide resin reaction product ofeither

i. the at least one bisimide of general formula I and at least oneprimary organic diamine or organic hydrazide, or

ii. the at least one bisimide of general formula I, at least onemonoimide, and at least one organic hydrazide,

then conveniently the co-reactant may also comprise, at least in part, aportion of the reagents of this reaction product, particularly if theeffect of the presence of these reagents is to reduce the melting pointand melt viscosity of the co-reactant and thereby render it moresuitable for use in the method of the present invention.

It is preferable that the TBN polymer be fully molten below 150° C.,preferably below 120° C., so that it can be intimately mixed with theimide resin co-reactant to allow copolymerisation to take place. It isessential that the TBN polymer is sufficiently compatible with theco-reactant for it to be at least partially mixable with the co-reactantsuch that copolymerisation can be substantially completed before theco-reactant reaches its gel point, although it is not essential that theTBN polymer and co-reactant be soluble in one another. The degree ofcompatibility is found to increase with increasing content of polargroups, i.e. acrylonitrile groups, in the TBN polymer. However, it isalso essential that the copolymer produced is sufficiently incompatiblewith the co-reactant such that it will form into phase separatedparticles within the mixture before the coreactant reaches its gelpoint. This copolymer incompatibility is found to decrease withincreasing acrylonitrile content, and so a compromise has to be found interms of VTBN acrylonitrile content. Preferably, therefore, the molarratio of butadiene groups to acrylonitrile groups in the TBN polymerlies in the range 99:1 to 65:35.

Where the TBN polymer is a VTBN, the VTBN may be selected from any ofthe different types of VTBN known in the art. Such a polymer has apolybutadiene/acrylonitrile backbone and terminal groups at both ends ofthe formula --C(R)═CH2 wherein R is independently selected from thegroup consisting of H and an alkyl group containing 1 to 4 carbon atoms.It may for example be of general formula VI ##STR8## where B is apolybutadiene/acrylonitrile polymeric backbone. Alternatively, the VTBNmay be of general formula VII ##STR9## where B is apolybutadiene/acrylonitrile polymeric backbone; Z is selected from--O--, --S--, --NH--, O--CO-- and --O--CH₂ --CH₂ --; A is selected from--CO--O--CH₂ --, --CH₂ --O--CH₂ -- and --CH₃ --O--; and each R isindependently hydrogen or an alkyl group containing 1 to 4 carbon atoms.This alternative group of VTBN's are described and claimed in U.S. Pat.Nos. 4,013,710 and 4,129,713.

Where the TBN polymer is a CTBN, the CTBN is preferably of generalformula VIB ##STR10## wherein the ratio of x to y lies in the range 99:1to 65:35.

In general, the lower the molecular weight of the TBN polymer, the loweris viscosity at a given temperature will be and the more likely it willmix with the molten resin. However, although the molecular weight of theTBN polymer is important in determining its fluid properties and henceits ability to mix with the resin, it also has other important effectson the reaction with the resin. The use of a TBN polymer of lowmolecular weight also enables a very large number of copolymerisationreactions to take place in the resin/elastomer mixture before phaseseparation of the imide copolymer takes place. This in turn facilitatesthe production of a highly toughened polyimide which better retains thethermal and oxidative properties of the polyimide per se than if a TBNpolymer of higher molecular weight were used. However, an undesirableeffect of decreasing the molecular weight of the elastomer is that thetime taken to achieve phase separation of the imide copolymer isgenerally increased, and this in turn increases the possibility of theresin matrix reaching its gel point before phase separation occurs. Itis therefore important to select a TBN polymer having a molecular weightwhich is generally as low as possible whilst still enabling phaseseparation of copolymer particles to take place before the resin matrixgels. Preferably, the molecular weight of the TBN polymer lies in therange 1000-10,000.

A number of analytical techniques may be used to demonstrate that, inthe reaction mixture comprising the TBN polymer and the reactant,copolymerisation followed by phase separation has taken place. Phaseseparation must take place before the co-reactant gels, because afterthat point the copolymer produced cannot migrate into particles, a factwell established in the art of toughening thermoset polymers by theaddition of elastomers. Firstly the rate of reduction of imide groupsmay be detected in a copolymerising mixture of the TBN polymer and theco-reactant, and, if greater than the rate of reduction of imide groupsin the co-reactant left to stand by itself at the same temperature, thisindicates that copolymerisation as well as homopolymerisation is takingplace in the reaction mixture. For example, the concentration of imidegroups may be measured in each sample using infra-red absorptiontechniques; any reduction in concentration will register as a reductionin one or more absorbed wavelengths unique to those imides present inthe mixture.

Scanning Electron Microscopy (SEM) may be used on the fractured faces ofportions of the sample, once cured, to detect the presence of solidphase separated particles therein. In detecting the presence ofparticles in the cured sample, SEM confirms that two solid phases existin the sample and, since neither CTBN nor VTBN polymers are known toundergo homopolymerisation, that one of the solid phases must thereforecomprise a copolymer of the resin and the elastomer. Furthermore, it maybe demonstrated by SEM that the volume fraction of the particles (incured samples of toughened polyimides prepared in accordance with thepresent invention) decreases with decreasing sample TBN content, provingthat the particle phase in the sample comprises or contains theresin/TBN copolymer. The term "phase separation"]as used in thisspecification includes the average diameter of the particles which formin the mixture of the resin and TBN is preferably between 0.1 and 10microns, most preferably 0.5 and 8 microns.

The volume fraction of the phase separated particle sin the polyimide ispreferably equal to or greater than the volume fraction of TBN in theliquid reaction mixture prior to copolymerisation.

The present invention further provides a method for preparing a fullycrosslinked polymer matrix containing a dispersion of phase-separatedsolid particles of copolymerised TBN polymer and coreactant, whichcomprises the further step of heating the thermosetting imide resincomposition prepared in accordance with the method of the first aspectof the present invention to a temperature between 100° C. and 350° C.

Polyimides cured from the thermosetting imide resin compositionsprepared in accordance with the first aspect of the present inventionare found to possess as much as 29 times the toughness (in terms ofincreased fracture energy), of polyimides cured from the correspondingimide resin-containing co-reactant alone. Furthermore, these novelelastomer-toughened polyimides are also invariably stronger and have thesame or even a higher glass transition temperature at the expense ofonly a moderately small decrease in decomposition temperature. Theoptimum concentration of TBN polymer in the imide resin compositionwhich produces polyimides having considerable improvements in toughnesswithout a significant reduction in glass transition temperature,decomposition temperature, and flexural modulus, lies in the range 10 to75 parts by weight of VTBN, or 10 to 50 parts of CTBN, per 100 parts ofco-reactant.

One further advantage of the method of the present invention is that theco-reactant need not necessarily be cured with the TBN polymer at apressure in excess of atmospheric pressure. Normally, addition-typepolyimide prepolymers (resins) have to be cured under pressure becausealthough the polymerisation reaction does not itself liberate anyvolatile byproducts, the prepolymers usually contain small amounts ofvolatile organic solvents which vaporise at typical polyimidepre-polymer curing temperatures, causing gas bubbles to form in theresultant polyimide matrix which is detrimental to the strength of thepolyimide. These solvents originate from the manufacture of theprepolymers, and their complete removal from the prepolymers prior tocuring is both difficult and expensive; hence most addition typepolyimide prepolymers will normally contain small quantities of thesesolvents as contaminants. Furthermore, where the polyimides are curedfrom mixtures of imide reagents and either hydrazide or diamine reagentsand the reaction products thereof in accordance with U.S. Pat. Nos.3,562,223, 4,211,860, 4,211,861, or 4,303,779, the problems of bubbleformation may be even more acute because the curing mixture may containreagents which are themselves volatile, especially if they containcertain organic diamines or organic hydrazides. It is now found that thepresence of a TBN polymer in accordance with the method of the firstaspect of the present invention suppresses gas formation, so that curingunder pressures in excess of atmospheric pressure is normallyunnecessary.

One yet further advantage of the first aspect of the present inventionis that the long-term tendency for the polyimide products of the presentinvention to absorb water is markedly reduced, so that the mechanicalproperties of the products at high temperature are maintained. Knownpolyimides will slowly absorb water from the atmosphere and othersources with time until they reach an equilibrium water content which istypically 5-10% by weight of the polyimide. This has the effect ofconsiderably reducing polyimide glass transition temperature (Tg) withtime.

According to a second aspect of present invention there is provided amethod for preparing a curable thermosetting prepolymerised imide resincomposition which comprises chemically reacting, at a temperature below150° C., a liquid mixture of a carboxy-terminatedpolybutadiene/acrylonitrile (CTBN) and a co-reactant comprising

(a) at least one N,N'-bisimide of an unsaturated carboxylic acid ofgeneral formula I ##STR11## wherein B represents a divalent radicalcontaining a carbon-carbon double bond and A represents a divalentradical having at least two carbon atoms, or

(b) the imide resin reaction product of at least one N,N'-bisimide ofgeneral formula I and at least one primary organic diamine or organichydrazide, or

(c) the imide resin reaction product of at least one N,N'bisimide ofgeneral formula I, at least one monoimide, and at least one organichydrazide,

to yield a curable thermosetting prepolymerised imide resin compositioncontaining copolymerised CTBN and co-reactant, said composition beingcurable at a temperature between 100° C. and 350° C. to a fullycrosslinked polyimide matrix containing a dispersion of phase-separatedsolid particles of copolymerised CTBN and co-reactant, said matrixhaving a lap shear strength at 20° C. at least 50% greater than that ofa fully crosslinked polyimide cured from the co-reactant alone.

Polyimides cured from the thermosetting imide resin compositionsprepared in accordance with the second aspect of the present inventionare found to possess as much as six times the toughness in terms ofincreased lap shear strength, or fourteen times the toughness in termsof increased fracture energy, of polyimides cured from the correspondingimide resin-containing co-reactant alone. Furthermore, these novelelastomer-toughened polyimides are also invariable stronger and have thesame or even a higher glass transition temperature at the expense ofonly a moderately small decrease in decomposition temperature. Theoptimum concentration of CTBN in the imide resin composition whichproduces polyimides having considerable improvements in toughnesswithout a significant reduction in glass transition temperature,decomposition temperature, and flexural modulus, lie sin the range 10 to50 parts by weight of CTBN per 100 parts of co-reactant.

It is essential to the method of the present invention that theco-reactant be fully molten below 150° C., preferably below 135° C., sothat it can be intimately mixed with the CTBN and so that the coreactantremains in an ungelled state for a sufficient length of time to allowthe CTBN to copolymerise with the co-reactant and form phase-separatedparticles in the reaction mixture within that time.

In the at least one bisimide of general formula I, the group B ispreferably selected from ##STR12## and most preferably the at least onebisimide comprises at least one of the following bisimides:

1,2-bismaleimido ethane,

1,4-bismaleimido butane,

1,6-bismaleimido hexane,

1,12-bismaleimido dodecane,

1,6-bismaleimido-(2,2,4-trimethyl)hexane,

1,3-bismaleimido benzene,

1,4-bismaleimido benzene,

4,4'-bismaleimido diphenyl methane,

4,4'-bismaleimido diphenyl ether,

4,4'-bismaleimido diphenyl sulfide,

4,4'-bismaleimido diphenyl sulfone,

4,4'-bismaleimido dicyclohexyl methane,

2,4- bismaleimido toluene,

2,6-bismaleimido toluene,

N,N'-m-xylylene bismaleimide,

N,N'-p-xylylene bismaleimide,

N,N'-m-phenylene biscitraconic acid imide,

N,N'-4,4'-diphenylmethane citraconimide, and

N,N'-4,4'-diphenylmethane bisitaconimide.

The co-reactant may comprise the reaction product of the at least onebisimide of general formula I and at least one primary organic diamineof general formula II

    H.sub.2 N--D--NH.sub.2                                     II

wherein D represents a divalent radical having not more than 3 carbonatoms, provided that the ratio of the total number of moles of bisimideof general formula I to the total number of moles of diamine of generalformula II in the reaction mixture lies in the range 1.2:1 to 50:1.Examples of diamines of general formula II which may be employed, are4,4'-diaminodicyclohexylmethane, 1,4-diaminocyclohexane,2,6-diaminopyridine, metaphenylene-diamine, paraphenylenediamine,4,4'-diaminodiphenylmethane, 2,2-bis(4-aminophenyl)propane, benzidine,4,4'-diaminophenyl oxide, 4,4'-diaminodiphenyl-sulphide,4,4'-diaminodiphenylsulphone, bis-(4-aminophenyl)di-phenylsilane,bis-(4-aminophenyl)methylphosphine oxide,bis-(3-aminophenyl)methylphosphine oxide, bis-(4-aminophenyl)phenylphosphine oxide, bis-(4-aminophenyl)phenylamine,1,5-diaminonaphthalene, metaxylylene-diamine, paraxylylene diamine,1,1-bis(paraaminophenyl)phthalene, and hexamethylenediamine.

Alternatively, the co-reactant may comprise the reaction product of theat least one bisimide of general formula I and at least one organichydrazide of general formula III ##STR13## wherein E represents adivalent organic group, provided that the ratio of the total number ofmoles of bisimide of general formula I to the total number of moles ofhydrazide of general formula III in the reaction mixture lies in therange of 1.1:1 to 1:1. Examples of hydrazides of general formula IIIwhich may be employed include

Oxalic acid dihydrazide,

malonic acid dihydrazide,

succinic acid dihydrazide,

glutaric acid dihydrazide,

adipic acid dihydrazide,

pimelic acid dihydrazide,

suberic acid dihydrazide,

sebacic acid dihydrazide,

cyclohexane dicarboxylic acid dihydrazide,

terephthalic acid dihydrazide,

isophthalic acid dihydrazide,

2,6-naphthalene dicarboxylic acid dihydrazide, and

2,7-naphthalene dicarboxylic acid dihydrazide.

The co-reactant may also comprise the reaction product of the at leastone bisimide of general formula I and at least one organic hydrazide ofgeneral formula IV ##STR14## wherein G represents a divalent organicgroup, provided that the total number of moles of bisimide of generalformula I to the total number of moles of hydrazide of general formulaIV lies in the range 1.1:1 to 10:1. Examples of hydrazides of generalformula IV which may be employed include

Amino acetic acid hydrazide,

alanine hydrazide,

leucine hydrazide,

isoleucine hydrazide,

phenyl alanine hydrazide,

valine hydrazide,

β-alanine hydrazide,

γ-amino butyric acid hydrazide,

α-amino butyric acid hydrazide,

ε-amino-caproic acid hydrazide,

amino valeric acid hydrazide,

and other aliphatic amino acid hydrazides.

Aromatic amino acid hydrazides such as

p-amino benzoic acid hydrazide,

p-amino benzoic acid hydrazide,

m-amino benzoic acid hydrazide,

anthranilic acid hydrazide, may also be used.

As a yet further alternative, the co-reactant may comprise the reactionproduct of the at least one bisimide of general formula I, at least onemonoimide of general formula V ##STR15## wherein B represents a divalentradical containing a carbon-carbon double bond and J represents analkyl, cycloalkyl, or aryl group, and at least one organic hydrazide ofgeneral formula III ##STR16## wherein E represents a divalent organicgroup. Examples of hydrazides of general formula III which may beemployed include

Oxalic acid dihydrazide,

malonic acid dihydrazide,

succinic acid dihydrazide,

glutaric acid dihydrazide,

adipic acid dihydrazide,

pimelic acid dihydrazide,

suberic acid dihydrazide,

sebacic acid dihydrazide,

cyclohexane dicarboxylic acid dihydrazide,

terephathalic acid dihydrazide,

isophthalic acid dihydrazide,

2,6-naphthalene dicarboxylic acid dihydrazide, and

2,7-naphthalene dicarboxylic acid dihydrazide.

Examples of monoimides of general formula V which may be employedinclude

N-methylmaleimide,

N-ethylmaleimide,

N-propylmaleimide,

N-dodecylmaleimide,

N-isobutylmaleimide,

N-isopropylmaleimide,

N-phenylmaleimide,

N-phenylcitroconimide,

N-phenylitaconimide,

N-toluylmaleimide,

N-mono-chlorophenylmaleimide,

N-biphenylmaleimide,

N-naphthlymaleimide,

N-vinylmaleimide,

N-allylmaleimide, and

N-cyclohexylmaleimide.

Where the co-reactant comprises the imide resin reaction product ofeither

i. the at least one bisimide of general formula I and at least oneprimary organic diamine or organic hydrazide, or

ii. the at least one bisimide of general formula I, at least onemonoimide, and at least one organic hydrazide,

then conveniently the co-reactant may also comprise, at least in part, aportion of the reagents of this reaction product, particular if theeffect of the presence of these reagents is to reduce the melting pointand melt viscosity of the co-reactant and thereby render it moresuitable for use in the method of the present invention. It is oneadvantage of the method of the present invention that when theco-reactant comprises a mixture of said reagents and reaction product,then this mixture after having been copolymerised need not necessarilybe cured with the CTBN at a pressure in excess of atmospheric pressurein order to suppress the formation of gas bubbles in the fullycrosslinked polyimide.

It is essential that the CTBN elastomer be fully molten below 150° C.,preferably below 120° C., so that it can be intimately mixed with theimide resin co-reactant to allow copolymerisation to take place. It isalso essential that the CTBN is sufficiently compatible with theco-reactant for it to be at least partially mixable with the co-reactantsuch that copolymerisation can be substantially completed before theco-reactant reaches its gel point, although it is not essential that theCTBN and co-reactant be soluble in one another. The degree ofcompatibility is found to increase with increasing content of polargroups, i.e. acrylonitrile groups, in the CTBN. However, it is alsoessential for the copolymer produced to be sufficiently incompatiblewith the co-reactant such that it will form into phase separatedparticles within the mixture before the coreagent reaches its gel point.This copolymer incompatibility is found to decrease with increasingacrylonitrile content, and so a compromise has to be found in terms ofCTBN acrylonitrile content. Preferably, therefore, the CTBN is ofgeneral formula VIB ##STR17## wherein the ratio of x to y lies in therange of 99:1 to 65:35.

In general, the lower the molecular weight of the carboxy-terminatedelastomer, the lower its viscosity at a given temperature will be andthe more likely it will mix with the molten resin. However, although themolecular weight of the carboxy-terminated elastomer is important indetermining its fluid properties and hence its ability to mix with theresin, it also has other important effects on the reaction with theresin. The use of an elastomer of low molecular weight also enables avery large number of copolymerisation reactions to take place in theresin/elastomer mixture before phase separation of the imide copolymertakes place. This in turn facilitates the production of a highlytoughened polyimide which better retains the thermal and oxidativeproperties of the polyimide per se than if an elastomer of highermolecular weight were used. However, an undesirable effect of decreasingthe molecular weight of the elastomer is that the time taken to achievephase separation of the imide copolymer is generally increased, and thisin turn increases the possibility of the resin matrix reaching its gelpoint before phase separation occurs. It is therefore important toselect a carboxy-terminated elastomer having a molecular weight which isgenerally as low as possible whilst still enabling phase separation ofcopolymer particles to take place before the resin matrix gels.Preferably, the molecular weight of the CTBN elastomer lies in the range1000-10,000.

A number of analytical techniques may be used to demonstrate that, inthe reaction mixture comprising the CTBN and the reactant,copolymerisation followed by phase separation has taken place. Phaseseparation must take place before the co-reactant gels, because afterthat point the copolymer produced cannot migrate into particles, a factwell established in the art of toughening thermoset polymers by theaddition of elastomers. Firstly the rate of reduction of imide groupsmay be detected in a copolymerising mixture of the CTBN and theco-reactant, and, if greater than the rate of reduction of imide groupsin the co-reactant left to stand by itself at the same temperature, thisindicates that copolymerisation as well as homopolymerisation is takingplace in the reaction mixture. For example, the concentration of imidegroups may be measured in each sample using infra-red absorptiontechniques; any reduction in concentration will register as a reductionin one or more absorbed wavelengths unique to those imides present inthe mixture.

Scanning Electron Microscopy (SEM) may be used on the fractured faces ofportions of the sample, once cured, to detect the presence of solidphase separated particles therein. In detecting the presence ofparticles in the cured sample, SEM confirms that two solid phases existin the sample and, since carboxy-terminated elastomers are not known toundergo homopolymerisation, that one of the solid phases must thereforecomprise a copolymer of the resin and the elastomer. Furthermore, it maybe demonstrated by SEM that the volume fraction of the particles (incured samples of toughened polyimides in accordance with the presentinvention) decreases with decreasing sample elastomer content, provingthat the particle phase in the sample comprises or contains the resinelastomer copolymer. The term "phase separation" as used in thisspecification includes the average diameter of the particles which formin the mixture of the resin and elastomer is preferably between 0.1 and10 microns, most preferably 0.5 and 8 microns.

The volume fraction of the phase separated particles in the polyimide ispreferably equal to or greater than the volume fraction of CTBN in theliquid reaction mixture prior to copolymerisation.

The present invention further provides a method for preparing a fullycrosslinked-polymer matrix containing a dispersion of phase-separatedsolid particles of copolymerised CTBN and co-reactant, said matrixhaving a lap shear strength at 20° C. at least 50% greater than that ofa fully crosslinked polyimide cured from the co-reactant alone, whichcomprises the further step of heating the prepolymerised resincomposition prepared in accordance with the method of the second aspectof the present invention to a temperature between 100° C. and 350° C.

Methods of preparing curable thermosetting prepolymerised imide resincompositions and of preparing polyimides cured therefrom in accordancewith the present invention will now be described by way of example only.

In Examples 1 to 8 inclusive, the imide resin co-reactant used was H353,which consists of a near-eutectic blend of three bismaleimide resinscomprising 4,4'-bismaleimido diphenyl methane, 2,4-bismaleimido-toluene,and 1,6-bismaleimido-(2,2,4-trimethyl)hexane. H353 is marketed byTechnochemie GmbH of West Germany. The H353 blend melts in the range 70°C. to 100° C., and is usually cured in the range 170° C. to 240° C.,though the minimum temperature at which it will gell over a long periodof time is about 120° C. to 135° C. In Examples 10 to 13 inclusive, theimide resin co-reactant used was H795, also marketed by TechnochemieGmbH, which consists of a mixture of an N,N'-bisimide, a hydrazide of anamino acid, and the imide resin reaction product thereof patented underU.S. Pat. No. 4,211,861. H795 has a melting point of about 110° C. andis usually cured at about 210° C. H353 and H795 have in more recenttimes been marketed under the trade names Compimide 353 and Compimide795 respectively.

The TBN polymers used in Examples 1 to 13 were all Hycar (Trade Mark)CTN elastomers marketed by the B F Goodrich Company, U.S.A. These CTNelastomers were all liquids at room temperature and had a molecularweight of about 3000 and a functionality of about 1.8. Hycar 1300×8 hadan acrylonitrile content of about 17% by weight, Hycar 1300×13 had anacrylonitrile content of about 26% by weight, and Hycar 1300×31 had anacrylonitrile content of about 10% by weight.

The following physical property tests were conducted on samples of fullycrosslinked polyimides prepared in accordance with the methods describedin Examples 1 to 13. Sample toughness was measured at 20° C. in terms offracture energy (C_(IC)) in Jm⁻² as determined by ASTM Standard MethodE399 1972 using samples prepared in a compact tension specimen geometry,and in terms of lap shear strength in MPa as determined by BritishStandard Specification 5350 Part C5 "Method of Tests for Adhesives".Increasing fracture energy and/or lap shear strength indicates anincrease in toughness. The flexural strength at failure and flexuralmodulus of elasticity of the samples was determined at room temperature(20° C.) by ASTM Standard Method D790-1971. The glass transitiontemperature (Tg) was determined by thermomechanical analysis using aStanton-Redcroft Thermomechanical Analyser. Tg indicated the temperatureat which a transition from hard elastic to soft rubbery or leathercharacteristics occurred in the samples with increasing temperature. Thedecomposition temperature (Td) of the samples was determined bythermogravimetric analysis on the samples in an atmosphere of either airor nitrogen, where the weight loss experienced by a sample wasconstantly monitored while sample temperature was raised at a prescribedrate. The temperature at which a 10% weight loss occurred was recorded.The average particle size of the phase separated solid particles formedwithin a sample was determined by first analysing the phase separatedparticles within a fractured face of the sample by Scanning ElectronMicroscopy (SEM), followed by estimating average particle size andoptionally volume fraction of particles within the sample, by subjectingthe analysis results to Spector's Method.

In Examples 14-18 and 21 the imide resin co-reactant used was Compimide353 which consists of a near-eutectic blend of three bismaleimide resinscomprising 4,4'-bismaleimido diphenyl methane, 2,4-bismaleimidotoluene,and 1,6-bismaleimido-(2,2,4-trimethyl) hexane. Compimide 353 is marketedby Technochemie GmbH of West Germany. The compimide 353 blend melts inthe range of 70° C. to 100° C., and is usually cured in the range 170°C. to 240° C., though the minimum temperature at which it will gel overa long period of time is about 120° C. to 135° C. In Example 19, theimide resin co-reactant used was Compimide 795, also marketed byTechnochemie GmbH, which consists of a mixture of an N,N'-bisimide, ahydrazide of an amino acid, and the imide resin reaction product thereofpatented under U.S. Pat. No. 4,211,861. Compimide 795 has a meltingpoint of about 100° C. and is usually cured at about 210° C. In Example20, the imide resin co-reactant was the reaction product of a diamineand a bismaleimide, which product is patented under and described inU.S. Pat. No. 3,562,223.

The VTBN used in Examples 14 to 20 was a Hycar (Trade Mark) elastomermarketed by the B F Goodrich Company, U.S.A. The Hycar elastomer usedwas Hycar 1300×22 VTBN, which is a liquid at room temperature, and has amolecular weight of about 3000, a functionality of about 1.8, and anacrylonitrile content of about 16% by weight. The VTBN used in Example21 differed from that used in Examples 14 to 20 in that it had anacrylonitrile content of about 27% by weight. It was prepared from Hycar1300×13 CTBN, a carboxy-terminated polybutadiene/acrylonitrile alsomarketed by B F Goodrich.

The following physical property tests were conducted on samples of fullycrosslinked polyimides prepared in accordance with the methods describedin Examples 14 to 21. Sample toughness was measured at 20° C. in termsof fracture energy (G_(IC)) in Jm⁻² as determined by ASTM StandardMethod E399 1972 using samples prepared in a compact tension specimengeometry, and in terms of lap shear strength in MPa as determined byBritish Standard Specification 5350 Part C5 "Method of Tests forAdhesives". Increasing fracture energy and/or lap shear strengthindicates an increase in toughness. The flexural strength at failure andflexural modulus of elasticity of the samples was determined at roomtemperature (20° C.) by ASTM Standard Method D790-1971. The glasstransition temperature (Tg) was determined by thermomechanical analysisusing a Stanton-Redcroft Thermomechanical Analyser. Tg indicated thetemperature at which a transition from hard elastic to soft rubbery orleather characteristics occurred in the samples with increasingtemperature. The decomposition temperature (Td) of the samples wasdetermined by thermogravimetric analysis on the samples in an atmosphereof either air or nitrogen, where the weight loss experienced by a samplewas constantly monitored while sample temperature was raised at aprescribed rate. The temperature at which a 10% weight loss occurred wasrecorded. The average particle size of the phase separated solidparticles formed within a sample was determined by first analysing thephase separated particles within a fractured face of the sample byScanning Electron Microscopy (SEM), followed by estimating averageparticle size and optionally volume fraction of particles within thesample, by subjecting the analysis results to Spector's Method.

EXAMPLE 1

H353 resin was heated to 120° C. until it became a low viscosity liquid.To 100 parts of this molten resin was added 10 parts by weight of liquidHycar 1300×8 elastomer also at 120° C. The resin and elastomer were thenthoroughly mixed, and the temperature of the mixture was maintained at120° C. for 24 hours, with occasional further mixing, to enable theelastomer to copolymerise with the resin. A reaction period of 24 hourswas chosen because it was known that at 120° C. H353 resin required atleast this period of time before reaching its gel point. The resin andelastomer were found not to be entirely compatible with one another atthis temperature, and so the further mixing was important to ensure thatintimate intermolecular contact between the resin and the elastomer wasmaintained throughout the 24 hour period, by breaking up the separatelayers of resin and elastomer which formed with time. The periods oftime between mixing were used to observe the gradual reduction in sizeof the elastomer layer as copolymerisation progressed. This elastomerlayer which formed on top of the resin was found to disappear altogetherafter about 24 hours, at which stage the copolymerisation reaction wastaken to be virtually complete.

During the 24 hours period, small samples of the mixture wereperiodically withdrawn, solidified by cooling, ground to powder, andsubjected to Infrared Spectroscopy using potassium bromide discs. Usingthis technique, the rate of reduction of imide groups in the mixture wasfollowed by measuring the reduction in the i.r. peak at 3100 cm⁻¹ (=3.23microns). A greater than expected rate of imide group consumption was afurther indication that the resin was copolymerising as well ashomopolymerising. After the completion of the copolymerisation stage,the product was degassed at 120° C. to remove air entrained duringmixing. The product was then gelled and cured to a fully crosslinkedpolyimide by first heating to 170° C. for two hours and then to 210° C.for a further five hours. The product was then brought back to roomtemperature by slowly cooling so as to prevent cracking. Fracturedsamples of the cured, cooled samples were subjected to SEM to reveal thepresence of phase separated solid particles in the polyimide. Theparticles were found to have an average size of about 5 microns.

EXAMPLE 2 TO 6 INCLUSIVE

The method of Example 1 was repeated in 5 further Examples, each using adifferent concentration of Hycar 1300×8 CTBN in the resin/elastomerreaction mixture to that used in Example 1. The CTBN concentrations usedwere: Example 2-30 phr, Example 3-50 phr, Example 4-100 phr, Example5-150 phr, and Example 6-200 phr. The term "phr" means part by weight ofCTBN per 100 parts by weight of H353 resin. In each Example, SEManalysis conducted on samples of the fully crosslinked polyimide productrevealed the presence of phase separated solid particles of average sizebetween 0.5 and 8 microns.

Samples of polyimide prepared in accordance with the methods of Examples1 to 6 inclusive were subjected to the physical property tests describedabove. The results of these tests are given in Table 1 below where theproperties are compared with those of samples of a Control Exampleprepared by fully crosslinking H353 alone using the same curingprocedure as employed in Example 1.

                                      TABLE 1                                     __________________________________________________________________________                Control                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                                                            Example                                         Example                                                                            1    2    3    4    5    6                                   __________________________________________________________________________    CTBN (phr)* 0    10   30   50   100  150  200                                 Fracture Energy G.sub.IC                                                                  11   45   140 ± 20                                                                        140 ± 60                                                                        470 ± 80                                   (Jm.sup.-2 @ 20° C.)                                                   Flexural Strength (MPa)                                                                   24   37   68 ± 8                                                                           63 ± 20                                                                         70 ± 10                                                                        >70  >70                                 Glass Transition                                                                          257  299  299  295  295                                           Temperature Tg (°C.)                                                   Decomposition                                                                          in air                                                                           562  530  508  516  481                                           Temperature Td                                                                         in N.sub.2                                                                       565  557  519  514  500                                           (°C., 10% wt loss)                                                     Flexural Modulus of                                                                       4.3  4.55 3.6  3.3  2.32    1.3                                                                                0.3                              Elasticity                                                                    (GPa @ 20° C.)                                                         Lap Shear Strength                                                                        4.05 8.0  18.45                                                                              24.86                                                                              26.22                                         (MPa at 20° C.)                                                        __________________________________________________________________________     *parts by weight of CTBN per 100 parts by weight of H353 resin           

From the results given in Table 1,it may be seen that polyimides curedfrom mixtures of H353 resin and Hycar 1300×8 CTBN prepared in accordancewith the present invention undergo, with increasing CTBN content, amarked increase in toughness together with a modest increase in flexuralstrength and glass transition temperature, up to a CTBN content of 100phr at least. The thermal stability of these toughened polyimides asmeasured by T_(D) is not unduly reduced in comparison with theuntoughened Control Example; however, a steady decline in flexuralmodulus is observed with increase CTBN content above a CTBNconcentration of 30 phr.

EXAMPLE 7

The method of Example 1 was repeated using 3 phr Hycar 1300×13 elastomerrather than 10 phr of Hycar 1300×8 elastomer. SEM analysis conducted onfractured samples of the fully crosslinked polyimide prepared inaccordance with the method of Example 7 revealed the presence of phaseseparated particles of average particle size between 0.5 and 8 microns,and the lap shear strength of a further sample of this polyimide wasmeasured at nearly six times that of corresponding sample of thepolyimide cured from H353 alone (the Control Example of Table 1 above).

EXAMPLE 8

To 100 parts by weight of 1,12 bismaleimido dodecane resin (mp 110°C.-120° C.) was admixed 30 parts by weight of Hycar 1300×31 elastomer ata temperature of 130° C. The resin had to be heated to at least 130° C.because below this temperature it was found to be too viscous tofacilitate mixing with the elastomer. The mixture was maintained for 8hours with occasional further mixing to effect copolymerisation betweenthe resin and the elastomer. A period of 8 hours was chosen because itwas known that at 130° C. the resin gelled after about 10 hours.

The imide resin product of the reaction was then cured to a fullycrosslinked polyimide by heating to 170° C. for 2 hours and then 210° C.for a further 5 hours. SEM analysis conducted on fractured samples ofthe cooled polyimide product revealed the presence of phase separatedparticles of average particle size between 0.5 and 8 microns, and thelap shear strength of a further sample of this polyimide was found to beat least 50% greater than that of a correspond sample of polyimide curedfrom 1,12 bismaleimido-dodecane alone using the same curing procedure.

EXAMPLE 9 (COMPARATIVE)

To 100 parts by weight of 4,4' bismaleimido diphenyl methane (mp 155°C.-180° C.) was admixed 30 parts by weight of Hycar 1300×8 elastomer ata temperature of 180° C. The bisimide resin had to be heated to 180° C.because below this temperature the elastomer could not easily be mixedin with it due to the resin's high viscosity. Once mixed with theelastomer, however, the mixture gelled within 20 minutes. The mixturewas then further cured to a fully crosslinked polyimide, and SEManalysis conducted on samples of the polyimide revealed the absence ofany detectable phase separated particles, indicating that phaseseparation had not taken place.

EXAMPLE 10

The method of Example 1 was repeated using H795 resin rather than H353resin.

EXAMPLES 11 to 13

The method of Example 10 was repeated in three further Examples, eachusing a different concentration of Hycar 1300×8 CTBN in theresin/elastomer reaction mixture to that used in Example 10. The CTBNconcentrations used were: Example 11-30 phr, Example 12-50 phr, andExample 13--100 phr, where "phr" means parts by weight of CTBN per 100parts by weight of H795.

Samples of polyimide prepared in accordance with the methods of Examples10 to 3 inclusive were tested to measure toughness and to detect thepresence of phase separated particles. In samples prepared in accordancewith each of these Examples, phase separated solid particles sizebetween 0.1 and 10 microns were detected by SEM analysis. The lap shearstrength of a sample of polyimide prepared in accordance with the methodof each of these Examples was found in all cases to be more than 50%greater than that of a sample of polyimide cured by the same curingsequence from H795 resin alone. The sample of H795 resin was, however,required to be cured under pressure to prevent the formation of gasbubbles in the polyimide, whereas those of the polyimides prepared bythe methods of Examples 10 to 13 inclusive were cured at atmosphericpressure without gas bubbles being detected in the polyimide matrix whencuring was complete.

EXAMPLE 14

Compimide 353 resin was heated to 120° C. until it became a lowviscosity liquid. To 100 parts of this molten resin was added 10 partsby weight of liquid Hycar 1300×22 VTBN elastomer also at 120° C. Theresin and elastomer were then thoroughly mixed, and the temperature ofthe mixture was maintained at 120° C. for 24 hours, with furtherthorough mixing every 1-2 hours, to enable the elastomer to copolymerisewith the resin. A reaction period of 24 hours was chosen because it wasknown that at 120° C. Compimide 353 resin required at least this periodof time before reaching its gel point. The resin and elastomer werefound not to be entirely compatible with one another at thistemperature, and so the further mixing was important to ensure thatintimate intermolecular contact between the resin and the elastomer wasmaintained throughout the 24 hour period, by breaking up the separatelayers of resin and elastomer which formed with time. The periods oftime between mixing were used to observe the gradual reduction in sizeof the elastomer layer as copolymerisation progressed. This elastomerlayer which formed on top of the resin was found to disappear altogetherafter about 24 hours, at which stage the copolymerisation reaction wastaken to be virtually complete.

After the completion of the copolymerisation stage, the product wasdegassed in vacuo at 120° C. to remove air entrained during mixing. Theproduct was then cast into preheated moulds, and finally gelled andcured at atmospheric pressure to a fully crosslinked, void-freepolyimide by first heating to 170° C. for two hours and then to 210° C.for a further five hours. The product was then brought back to roomtemperature by slowly cooling so as to prevent cracking. Fracturedsamples of the cured, cooled product were subjected to SEM to reveal thepresence of phase separated solid particles in the polyimide. Theparticles were found to have an average size 0.1 to 10 microns.

EXAMPLES 15 TO 18

The method of Example 14 was repeated using respectively 30 parts(Example 15), 50 parts (Example 16) 75 parts (Example 17) and 100 parts(Example 18) by weight of Hycar 1300×22 VTBN per 100 part of Compimide353 in the resin/elastomer reaction mixture. SEM analysis conducted onsamples of the fully crosslinked void-free polyimide product revealedthe presence of phase separated solid particles of average size between0.1 and 10 microns.

Samples of polyimide prepared in accordance with the methods of Examples14 to 18 were subjected to the physical property tests described above.The results of these tests are given in Table 2 below where theproperties are compared with those of samples of a Control Exampleprepared by fully crosslinking Compimide 353 alone using the same curingprocedure as employed in Example 14.

                                      TABLE 2                                     __________________________________________________________________________    Example     Control                                                                            1   2    3     4    5                                        __________________________________________________________________________    VTBN (phr)* 0    10  30   50    75   100                                      Fracture Energy G.sub.IC                                                                  11   29 ± 3                                                                         50 ± 10                                                                         193 ± 6                                                                          322 ± 73                                   (Jm.sup.-2 @ 20° C.)                                                   Flexural Strength (MPa)                                                                   24   29 ± 3                                                                         39 ± 4                                                                           64 ± 15                                                                         84 ± 7                                     Glass Transition                                                                          257      290  285   245                                           Temperature Tg (°C.)                                                   Decomposition                                                                          in air                                                                           562      514  502                                                 Temperature Td                                                                         in N.sub.2                                                                       565      523  517                                                 (°C., 10% wt loss)                                                     Flexural Modulus of                                                                       4.3  4.6 3.8  3.2   2.78                                          Elasticity                                                                    (GPa @ 20° C.)                                                         Lap Shear Strength                                                                        4.05 6.33                                                                              6.73 9.57  11.23                                                                              12.38                                    (MPa at 20° C.)                                                        __________________________________________________________________________     *parts by weight of VTBN per 100 parts by weight of Compimide 353 resin. 

From the results given in Table 2, it may be seen that polyimides curedfrom mixtures of Compimide 353 resin and Hycar 1300×22 VTBN prepared inaccordance with the present invention undergo, with increasing VTBNcontent, a marked increase in toughness together with a modest increasein flexural strength and glass transition temperature, up to a VTBNcontent of 50 parts per hundred (phr) at least. The thermal stability ofthese toughened polyimides as measured by T_(D) is not unduly reduced incomparison with the untoughened Control Example.

EXAMPLE 19

The method of Example 14 was repeated using Compimide 795 resin insteadof Compimide 353 resin, and 50 phr (parts per hundred by weight) ofHycar 1300×22 VTBN.

Samples of polyimide prepared in accordance with the method of Example19 were tested to measure toughness and to detect the presence of phaseseparated particles. Phase separated solid particles of average sizebetween 0.1 and 10 microns were detected by SEM analysis. The polyimideprepared by the method of Example 19 was cured at atmospheric pressurewithout gas bubbles being detected in the polyimide matrix when curingwas complete. The Fracture Energy G_(IC) of the samples of polyimideprepared in accordance with the method of Example 19 was measured at400±20 Jm⁻² at 20° C., and their average Flexural Modulus of Elasticitywas measured at 2.0 GPa at 20° C.

EXAMPLE 20

A polyimide prepolymer co-reactant was prepared in accordance with theinvention described in U.S. Pat. No. 3,562,223. 300 grams of Compimide353 resin was first ground to a powder at room temperature in a mortarand pestle. To the ground powder was admixed 30 grams of diaminodiphenyl sulphone powder. The mixture was then ground to a fine powderin a ball mill for 1 hour, using 6-18 mm diameter ceramic ballsrevolving in an 8 cm diameter drum at 50 revolutions per minute. Theresulting fine, powdered mixture was then melted at 120° C. for 1 hourwith occasional mixing, to produce the required molten co-reactantresin.

165 grams of Hycar 1300×22 VTBN at 120° C. was admixed to the moltenco-reactant at 120° C., producing a molten mixture containing 30 phr ofVTBN. The molten mixture was maintained at 120° C. for 8 hours, withfurther thorough mixing approximately every hour during the 8 hours,until the separate VTBN elastomer layer which formed on top of the resinlayer had disappeared, indicating that the VTBN/resin copolymerisationreaction was completed. The copolymerised mixture was degassed undervacuum for 30 minutes at 120° C., and was then cast into preheatedmoulds also at 120° C. The cast mixture was first gelled and then curedto a fully cross-linked, void-free polyimide by heating at atmosphericpressure to 170° C. for 2 hours and then to 210° C. for a further 5hours, and subsequently slowly cooling the product to room temperature.

Fractured samples of the cured, cooled product were subjected to SEM toreveal the presence of phase separated solid particles of average sizebetween 0.1 and 10 microns in the polyimide product. The lap shearstrength of samples of the product was found in all cases to be greaterthan that of a sample of polyimide cured from the co-reactant alone bythe same curing sequence as described above though at a pressure well inexcess of atmospheric pressure in order to suppress bubble formation.The average Fracture Energy G_(IC) of the samples of polyimide preparedin accordance with the method of Example 20 was measured at 223 Jm⁻² at20° C., and their average Flexural Modulus of Elasticity was measured at1.9 GPa at 20° C.

EXAMPLE 21

The method of Example 14 was repeated using 30 phr VTBN containing about27% acrylonitrile by weight. This VTBN was prepared from 27%acrylonitrile carboxy-terminated polybutadiene/acrylonitrile marketed asHycar 1300×13 CTBN by B F Goodrich, by the known reaction proceduregenerally outlined in U.S. Pat. Nos. 4,129,713 and 4,013,710. Phaseseparated solid particles of average size 0.1 to 10 of the product wereas follows:

    ______________________________________                                        Fracture Energy:     51.7 Jm.sup.-2 at 20° C.                          Flexural Strength:   72 ± 25 MPa                                           Glass Transition Temperature:                                                                      275° C.                                           Flexural Modulus of Elasticity:                                                                    3.14 GPa at 20° C.                                ______________________________________                                    

We claim:
 1. A method for preparing a thermosetting imide resincomposition which comprises chemically reacting a liquid mixture of avinylidene terminated polybutadiene/acrylonitrile (VTBN) polymer havinga polybutadiene/acrylonitrile backbone and terminal groups at both endsof the formula --C(R)═CH₂ wherein R is independently selected from thegroup consisting of H and an alkyl group containing 1 to 4 carbon atoms,with a co-reactant selected from the group consisting of:(a) at leastone N,N'-bisimide of an unsaturated carboxylic acid of the formula I##STR18## wherein B represents a divalent radical containing acarbon-carbon double bond and A represents a divalent radical having atleast two carbon atoms, (b) the imide resin reaction product of at leastone N,N'-bisimide of formula I and at least one primary organic diamineor organic hydrazide, and (c) the imide resin reaction product of atleast one N,N'-bisimide of formula I, at least one monoimide, and atleast one organic hydrazide,to yield a thermosetting imide resincomposition containing copolymerised VTBN and co-reactant, saidcomposition being curable at a temperature between 100° C. and 350° C.to a fully cross-linked polyimide matrix containing a dispersion ofphase separated solid particles of copolyermised VTBN and co-reactant.2. A method according to claim 1 wherein the average particle size ofthe phase separated particles, as determined by Scanning ElectronMicroscopy, lies in the range 0.1 to 10 microns, preferably 0.5 to 8microns.
 3. The method according to claim 1 wherein the co-reactantcomprises the reaction product of at least one N,N'-bisimide of formulaI wherein A and B are as defined in claim 1, and at least one primaryorganic diamine of formula II

    H.sub.2 N--D--NH.sub.2                                     (II)

wherein D represents a divalent radical having not more than 30 carbonatoms, and wherein the ratio of the total number of moles of bisimide offormula I to the total number of moles of diamine of formula II in thereaction mixture lies in the range 1.2:1 to 50:1.
 4. A method accordingto claim 1 wherein the co-reactant comprises the reaction product of atleast one N,N'-bisimide of formula I, wherein A and B are as defined inclaim 1, and at least one organic hydrazide of formula III ##STR19##wherein E represents a divalent organic group, and wherein the ratio ofthe total number of moles of bisimide of formula I to the total numberof moles of hydrazide of formula III in the reaction mixture lies in therange 1.1:1 to 10:1.
 5. A method according to claim 1 wherein theco-reactant comprises the reaction product of at least one N,N'-bisimideof formula I, wherein A and B are as defined in claim 1, and at leastone organic hydrazide of formula IV ##STR20## wherein G represents adivalent organic group, and wherein the total number of moles ofbisimide of formula I to the total number of moles of hydrazide offormula IV lies in the range 1.1:1 to 10:1.
 6. A method according toclaim 1 wherein B represents a group selected from the group consistingof ##STR21##
 7. A method according to claim 1 wherein the at least onebisimide of general formula I comprises at least one of the followingbisimides1,2-bismaleimido ethane, 1,4-bismaleimido butane,1,6-bismaleimido hexane, 1,12-bismaleimido dodecane,1,6-bismaleimido-(2,2,4-trimethyl)hexane, 1,3-bismaleimido benzene,1,4-bismaleimido benzene, 4,4'-bismaleimido diphenyl methane,4,4'-bismaleimido diphenyl ether, 4,4'-bismaleimido diphenyl sulfide,4,4'-bismaleimido diphenyl sulfone, 4,4'-bismaleimido dicyclohexylmethane, 2,4- bismaleimido toluene, 2,6-bismaleimido toluene,N,N'-m-xylylene bismaleimide, N,N'-p-xylylene bismaleimide,N,N'-m-phenylene biscitraconic acid imide, N,N'-4,4'-diphenylmethanecitraconimide, and N,N'-4,4'-diphenylmethane bisitaconimide.
 8. A methodaccording to claim 1 wherein the molar ratio of butadiene groups toacrylonitrile groups in the VTBN polymer lies in the range 99:1 to65:35.
 9. A method according to claim 1 wherein the VTBN polymer is aVTBN of general formula VIA ##STR22## wherein B is apolybutadiene/acrylonitrile polymeric backbone.
 10. A method accordingto claim 1 wherein the VTBN polymer is a VTBN of Formula VII ##STR23##wherein B is a polybutadiene/acrylonitrile polymeric backbone; Z isselected from the group consisting of --O--, --S--, --NH--, --O--CO--,and --O--CH₂ --CH₂ --; A is selected from the group consisting of--CO.--O--CH₂ --, --CH₂ --O--CH₂ --, and --CH₂ --O--; and each R isindependently hydrogen or an alkyl group containing 1 to 4 carbon atoms.11. A method according to claim 1 wherein the matrix has a lap shearstrength at 20° C. at least 50% greater than that of a fullycross-linked polyimide cured from the co-reactant alone.
 12. A methodaccording to claim 1 which further comprises the subsequent step ofheating the thermosetting imide resin composition to a temperaturebetween 100° C. and 350° C. to yield a fully cross-linked polymer matrixcontaining a dispersion of phase-separated solid particles ofcopolymerised VTBN polymer and co-reactant.
 13. A thermosetting imideresin composition prepared by the method according to claim
 1. 14. Afully cross-linked polyimide matrix containing a dispersion ofphase-separated solid particles of TBN polymer and co-reactant preparedby the method of claim 12.